The present invention relates to a tractor protection function for an articulated vehicle. It finds particular application in conjunction with using an electronically controlled modulator for providing the tractor protection function and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other applications.
Air brake systems are commonly used for articulated vehicles including a tractor that tows at least one trailer. Such systems include a tractor protection valve that controls air supply to brakes on the trailer. The tractor protection valve receives an air signal from a park brake control valve that is typically mounted to a dash (e.g., a dashboard) in the tractor. The air signal from the park brake control valve can be used to apply or release trailer spring brakes, which are also referred to as trailer parking or trailer emergency brakes, and can be used to charge or re-supply trailer reservoirs, which normally comprise primary and secondary air sources on the tractor. The tractor protection valve also receives air signals from a service brake foot valve and/or a trailer hand control valve, which are utilized by an operator of the vehicle to apply or release trailer service brakes.
If there is insufficient air pressure in the parking brake or re-supply portion of the tractor protection valve, the tractor protection valve is configured to prevent air from being delivered from the tractor to the trailer through a service brake portion of the tractor protection valve. This prevents both the parking and service brakes being simultaneously applied (e.g., compounding of the trailer spring brakes) and protects a tractor air supply by blocking a loss of air pressure out of a service control line in the event that a connection line between the tractor and trailer is inadvertently disconnected or a leak exists in the trailer air line.
Conventionally, the tractor protection function is achieved using a dedicated pneumatic tractor protection valve on the tractor for protecting air loss in the above-described situations. The service brake portion of the pneumatic tractor protection valve includes a normally-closed valve for controlling communication of the air from the tractor for controlling the trailer service brakes. The normally-closed valve only opens when sufficient pressure is present in the parking brake or re-supply portion of the tractor protection valve.
The present invention provides a new and improved apparatus and method for protecting air supplied from a tractor to a trailer in the event a connection line between the tractor and trailer is disconnected or a leak exists in the trailer air line.